Transmission devices known per se and designed as automatic transmissions, such as a multi-stage transmission described for example in DE 10 2005 002 337 A1, are constructed in order to obtain various gear ratios with shifting elements by means of which in each case an applied torque can be transmitted by frictional means. When the engagement of a particular gear ratio has been called for, in each case at least one or more of the frictional shifting elements are disengaged from the force flow of a transmission device while at least one further frictional shifting element, or others, are engaged in the force flow of the transmission device in order to obtain the required gear ratio. During the process of engaging a frictional shifting element, no special synchronization measures are needed to ensure a desired level of shifting comfort, since with frictional shifting elements a desired shifting comfort can be achieved at defined contact pressures within a broad band of rotational speed differences. Automatic transmissions so constructed are disclosed in both WO 2008/138732 A1 and DE 102 44 023 A1.
Since in a manner known per se such transmission devices can only be operated with unsatisfactory efficiencies because of drag losses that occur in the area of open frictional shifting elements, certain frictional shifting elements are replaced by interlocking shifting elements. In such automatic transmissions, which are made with both frictional shifting elements and at least one interlocking shifting element and with a corresponding gearset configuration, to implement a particular shift command at least one interlocking shifting element has to be engaged in a force flow of the transmission device.
Disadvantageously, compared with frictional shifting elements, interlocking shifting elements with or without additional structural synchronization devices can only be engaged comfortably at very low speed differences, i.e. close to their synchronous rotational speed, and this impairs to an undesired extent the operation of a transmission device designed as an automatic transmission and comprising at least one interlocking shifting element, at any rate while carrying out certain gearshifts that involve an interlocking shifting element. In some circumstances a shift operation called for can only be completed after the lapse of an undesirably long shifting time, since before the interlocking shifting element involved in producing the gearset called for is engaged, the speed difference in the area of the interlocking shifting element has to be adjusted to a value at which the interlocking shifting element can be shifted to its engaged operating condition.
However, additional structural measures for synchronizing interlocking shifting elements of transmission devices so as to be able to carry out a required shift within an acceptable shifting time along with a high level of shifting comfort, undesirably increase both the manufacturing costs of transmission devices and the space they occupy.